The use and construction of optical fiber cables, and optical fiber buildouts used for coupling optical fiber cables together is well known. Optical fiber cables are provided with optical fiber connectors at their ends, the optical fiber connectors being one of several known types of connectors, namely either an SC, an ST.RTM., an FC, and/or an LC type of optical fiber connector. The SC, ST and FC connectors are provided with 2.5 mm diameter ferrules, whereas the LC type of optical fiber connectors are provided with a 1.25 mm diameter ferrule.
When it is desired to terminate an optical fiber cable, the cable is cut and stripped leaving an exposed portion of the optical fiber. The exposed optical fiber is passed within an elongate bore defined in, and extending along the longitudinal axis of a connector ferrule. The ferrule typically comprises either a rigid plastic or ceramic material, ceramic being preferred. The ferrule forms a part of the optical fiber connector of one of the types described above, such that it can be coupled to either a buildout base or cap, and the cap or base then coupled to one another for making the optical fiber coupling.
A problem that arises in making these optical fiber couplings, however, lies in the fact that the bore defined within the ferrule may have some eccentricity about the longitudinal axis of the ferrule, such that, although on a microscopic level, for example on the order of 9 microns, there may be some misalignment between the optical fibers housed within two respective ferrules as they are coupled to one another. This will result in an unintended or unexpected reduction in the value of the optical signal passed therethrough.
U.S. Pat. Nos. 4,738,507 and 4,738,508 to Palmquist, both of which are assigned to AT&T Technologies, Inc., the predecessor in interest to the assignee of this invention, each respectively disclose methods of identifying in which quadrant of the ferrule, about its longitudinal axis, the eccentricity of the optical fiber lies. This eccentricity, once identified is then keyed to a key or marker on the optical fiber connector or grip, such that when a connection is made between two similarly marked optical fiber connectors the amount of eccentricity between the ends of two adjacent coupled optical fibers is hopefully minimized for allowing the greatest possible value of the optical signal to be passed therethrough. Although the method, and optical fiber connectors of Palmquist have proven to be extremely useful in terms of identifying these eccentricities, and minimizing the impact of these eccentricities when making fiber optic connections in the field, they have the drawback of requiring that this be done in a controlled environment, for example in a production facility, and which method is not capable of being easily performed in the field for selectively optimizing, or attenuating signals, as desired.
An improvement to the concept of Palmquist is disclosed in U.S. Pat. No. 5,212,752 to Stephenson, et al., also assigned to AT&T Bell Laboratories, in which an optical fiber ferrule connector having enhanced provisions for tuning an SC type of connector is provided. The eccentricity of the ferrule passageway is tuned to the plug frame of the optical fiber connector, and more particularly to a key or mark on the plug frame, whereupon the plug frame is then assembled to the grip in alignment with the usual key thereon which identifies the quadrant in which the eccentricity is found.
What, however, this patent to Stephenson, et al. does not provide, is the ability to utilize these eccentricities to selectively tune the optical fiber connection in the field by either attenuating, or optimizing the value of the optical signal, as desired. The need exists, therefore, for an improved optical fiber buildout assembly which will quickly and easily overcome, and/or make advantageous use of these ferrule eccentricities, and which can be used with any one of the several different types of buildout bases and buildout caps.